e.clientX：指鼠标距离浏览器左边的距离
e.clientY：指鼠标距离浏览器上边的距离
div.offsetTop： div元素到距离浏览器可视化窗口上边的距离
div.offsetLeft： div元素到距离浏览器可视化窗口左边的距离
wps2.jpeg
wps1.jpeg
如果要设置物体拖拽，那么必须使用三个事件，并且这三个事件的使用顺序不能颠倒。
1、onmousedown：鼠标按下事件
2、onmousemove：鼠标移动事件
3、onmouseup：鼠标抬起事件
注：
1、一定要绝对定位
2、onmousedown绑定拖拽的元素，onmousemove和onmouseup是针对document的绑定，因为移动的是整个div
3、计算
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<style>
#box {
width: 400px;
height: 150px;
background: purple;
position: absolute;
cursor:move;
}
</style>
<body>
<div id="box"></div>
<script>
window.onload = function () {
var box = document.getElementById('box');
box.onmousedown = function (e) {
e = event || window.event;
var diffX = e.clientX - box.offsetLeft;
var diffY = e.clientY - box.offsetTop;
//修复低版本ie bug
if(typeof box.setCapture !== 'undefined'){
box.setCapture();
}
document.onmousemove = function (e) {
e = event || window.event;
var moveX = event.clientX - diffX;
var moveY = event.clientY - diffY;
// 边界判断
if (moveX < 0) {
moveX = 0;
}else if (moveX > window.innerWidth - box.offsetWidth){
moveX = window.innerWidth - box.offsetWidth;
}
if (moveY < 0) {
moveY = 0;
}else if (moveY > window.innerHeight - box.offsetHeight) {
moveY = window.innerHeight - box.offsetHeight;
}
// 关键性赋值绝对定位top left距离
box.style.left = moveX + 'px';
box.style.top = moveY + 'px';
}
// 鼠标抬起，清楚绑定再文档上的mousemove和mouseup事件，否则鼠标抬起后还可以继续拖拽方法
document.onmouseup = function (e) {
e = event || window.event;
this.onmousemove = null;
this.onmouseup = null;
//修复低版本ie bug
if(typeof box.releaseCapture!='undefined'){
box.releaseCapture();
}
}
}
}
</script>
</body>
</html>
// 转自：https://blog.csdn.net/weixin_41910848/article/details/82218243
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